1. Field of the Invention
This invention relates to an analytical technique used in the manufacture of semiconductor devices, and more particularly, it relates to a method for determining the presence of a thin insulating film. The method can be employed in confirming the removal of insulating films formed on electrically conductive materials such as semiconductors and metals.
2. Description of the Prior Art
Hitherto various techniques have been used in determining the presence of any residual insulating film after the removal thereof from the surface of electrically conductive materials.
For example, a method utilizing the water repellency method has often been employed in determining the presence of any residual oxide film after the removal thereof from the surface of silicon by chemical treatment (see, for example, R. Williams et al., Appl. Phys. Lett., Vol. 25, No. 10, 15 Nov. 1974, pp. 531-532).
As shown in FIG. 19, this technique is a simple method by which the thickness d of an oxide film 10 present on the surface of a silicon substrate 8 can be determined by the value of the contact angle 0 between the surface of the oxide film 10 and the line drawn tangent to the surface of a water droplet 27 where it meets the surface of the oxide film 10 on the silicon substrate 8.
FIG. 20 shows the relationship between the value of cos .theta. and the thickness d of the residual oxide film. As can be seen from FIG. 20, it is possible to make a qualitative determination that the residual oxide film 10 is thinner as the water droplet 27 is more easily repelled or as the contact angle .theta. is greater. In this way, a rough basis for determination of the presence of oxide films can be readily obtained, therefore, the above-mentioned method has often been used in conjunction with fabrication processes for semiconductor deices.
Beside the water repellency method mentioned above, there have been employed various other methods intended to more closely determine the presence of any residual oxide film on the surface of silicon through instrumental analyses, including Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), energy dispersion type X-ray microanalysis method (EDX), ion scattering spectroscopy (ISS), and X-ray photoelectron spectroscopy (XPS). These techniques for instrumental analyses have already been so advanced as to make possible the quantitative determination of any residual insulating film present on the silicon surface, which can be applied to the analysis with respect to any combination of materials other than the above-mentioned combination of silicon and oxide film. These techniques have therefore been employed when high accuracy is required of such determination.
However, these conventional techniques have the following disadvantages:
(1) The techniques for instrumental analyses, although they permit quantitative analyses with high accuracy, require a vacuum chamber and other large-scale instruments. In addition, a relatively long period of time is required before analysis results can be obtained.
(2) The techniques for instrumental analyses must be used as a destructive analysis technique.
(3) The water repellency method is a nondestructive analysis technique and very simple. However, this method is qualitative and can provide nothing but rough measurements. For example, it is quite difficult to accurately measure the actual value of .theta. shown in FIG. 19. In fact, when the water droplet on the silicon substrate 8 is found to be readily repelled, by a visual inspection, it is possible to determine macroscopically that the oxide film has been removed; however, it is impossible to determine microscopically what thickness the residual oxide film 10 has. As seen from FIG. 20, the definite determination as to the presence of any residual oxide film is limited to a thickness of more than 12 .ANG.. Therefore, if device fabrication proceeds to a next step only on the basis of a visual inspection when a very thin oxide film still remains, considerable difficulties may be caused from the standpoint of product reliability.